Electrically heated annealing furnace base



Nov. 16, 1954 E. E. RICE ET AL ICALLY HEATED ANNELING FURNACE BASE 3Shees-Sheet l Filed June 17, 1953 i r if@ fire. 4.

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ELECTRICALLY HEATED ANNEALING FURNACE BASE 3 Sheets-Sheet 2 Filed June17 QTY'ORNEYSv NOV. 16, 1954 E. E RlCE ETAL ELECTRIGALLY HEATEDANNEALING FURNACE BASE 3 Sheets-Sheet 3 Filed June 17, 1953 INVENTORdC-06.4K E H65 /rr//En/J Fa/.EK

ATTORNEYS.

United States Patent O ELECTRICALLY HEATED ANNEALING FURNACE BASE EdgarE. Rice, Butler, Pa., and Matthew J. Foley, Middletown, Ohio, assignorsto Armco Steel Corporation, Middletown, Ohio, a corporation of OhioApplication June 17, 1953, Serial No. 362,280

14 Claims. (Cl. 13-25) This invention relates to an electrically heatedannealing furnace base and is a continuation-in-part of our copendingapplication, Serial Number 302,074, tiled August 1, 1952, and nowabandoned. In the treatment of various kinds of steels they aresometimes subjected to what is known as a box anneal where the steelpieces are suitably disposed upon a refractory base, and thereupon abox-like structure is lowered over the steel pieces. Means are providedto heat the interior of the box and lsjometimes special atmospheres areintroduced into the In connection with the annealing of steel coilscertain additional problems arise which are not encountered inconnection with sheets. Furthermore, where these coils are of siliconsteel, the additional problem arises that the annealing temperatures areabove 2000 F., and that these high temperatures necessitate electricheating.

There have been annealing bases in the art where heat was provided inthe base. This has generally been accomplished by means of tubes throughwhich steam was passed, and heating of the coils was accomplished byradiation.

There have also been bases for annealing furnaces where electric heatingwas provided, but this type of structure is not satisfactory at the hightemperatures encountered with silicon steel and with the tremendousloads where silicon steel coils are stacked on top of each other, as isthe present practice.

With the foregoing considerations in mind, it is an object of thepresent invention to provide a base for an annealing furnace which willhave a high strength so 1that it will readily support double-stackedheavy co1 s.

It is another object of the invention to provide for electric heatingelements in the base and to dispose the heating elements in such a waythat the heating elements will not be burned out either by contactingthe low heat absorbing refractory material of the base which would causefailure because of the inability of the base material to absorb the highheat, or because of a short circuit, which would result in theliberation of excess heat.

The supporting structure for the heating element is so arranged that ahigh and efficient heat transfer by radiation is accomplished.

It is still another object of the invention to make it possible to useconductive or somewhat conductive material for the base by providinginsulating means to space the electrical element from the load-bearingrefractories.

These and various other objects of the invention, which will be pointedout in greater detail hereinafter, or which will be apparent to oneskilled in the art upon reading these specifications, we accomplish bythat certain construction and arrangement of parts, of which we shallnow disclose certain exemplary embodiments.

Reference is here made to the drawings forming a part hereof, and inwhich:

Figure l is a plan view of an annealing furnace base according to ourinvention with the cover removed;

Figure 2 is a front elevational view of the same showing the annealingcover in broken lines;

Figure 3 is a longitudinal vertical cross sectional view through anannealing cover showing the heating means in the walls thereof;

Figure 4 is a fragmentary cross sectional View on a greatly enlargedscale taken on a line 4-4 of Figure l;

Figure 5 is a diagram showing the arrangement of the heating element inthe base;

Figure 6 is a cross sectional view on an enlarged scale taken on a line6 6 of Figure 2;

Figure 7 is a fragmentary plan view of the base without the spools orcoils stacked thereon, as seen substantially on the line 7-7 of Figure6;

Flgure 8 is a fragmentary cross sectional view on a grealy enlargedscale taken on the line 8-8 of Figure Fitgure 9 is a perspective view ofan insulating elemen Figure l0 is a cross sectional view taken on theline 10-710 of Figure 9;

Figure l1 is a perspective view of one of the refractory base elements;

Flgure 12 is a fragmentary plan view similar to Figure 7 on a greatlyenlarged scale;

Figure 13 is a plan view of a modification of an annealing baseaccording to the invention, with the cover removed;

Figure 14 is a cross 14-14 of Figure 13;

Figure 15 is a fragmentary enlarged view of a portion of Figure 14; and

Figure 16 is an elevational view of a modified insulating element.

By way of illustration, we have disclosed an annealing furnace of a sizearranged to accommodate three stacks of standard coils, the stacks eachcomprising two coils one on top of the other. lt will be understood thatthe annealing furnace and its base may be designed for any desirednumber of stacks, and the showing herein is by way of example only.

Reference is made to Burdette, U. S. Patent No. 2,490,412, as to detailsof the spool and supporting column whereby the two coils are stacked oneon top of the other.

The furnace base may be mounted on a structural steel frameworkindicated generally at 10. On top of this structural steel frameworkthere is provided a refractory base built up of several layers ofrefractory brick of conventional form, and indicated generally at 11. Acoping wall of refractory material is indicated at 12, and conventionalsand or other sealing structure is indicated generally at 13. A fragmentof the annealing cover is shown at 14 in Figure 4. As is well known,when the annealing cover 14 is placed in position, an element projectingdownwardly from the edges thereof enters into a sand pocket formed inthe base to provide a seal so that special atmospheres may be providedwithin the furnace during the processing of the steel. The variouselements just described forming no part of the present invention willnot be described further. Similarly, the details of the annealing coverwill not be entered into in detail, although from Figure 3 it will beapparent that the cover is lined with a refractory material, as at 15,and is provided with heating coils 16 on its inside walls. Suspensionmeans whereby the cover may be emplaced and removed are indicated at 17.

ln view of the fact that this particular furnace is arranged for threestacks of coils which are circular in projection on the horizontalplane, the heating elements which are arranged in a zig-zag pattern maybe arranged to provide three generally circular outlines which will fallunder the three stacks of coils as indicated in Figure 5 at A, B and C,or they may be in substantially rectangular formations as shown inFigure 13.

In placing the coils on the base the lowermost coil of each stack willbe placed upon a stool or base 18, which has a central hole 19 and acolumn 20 will be placed thereon to support an upper stool upon which anupper coil may rest. The upper stool is indicated at 21. The upper stoolmay also be provided with a column as at 22 so that the stack may bemade higher, and so that the stools may be interchangeable.

On top of the various layers 11 of refractory material we lay a finallayer of refractory elements which may conform to the circular outlineof the projection of the stools 18 upon the base as in Figures l to 12,or which may be arranged in a rectangular configuration as in Figure 13.One form of these elements is shown in detail in perspective in Figure11 and in this form they sectional view taken on the line comprise" arectangular` base portion 30, above which there is'the upwardlyextending tapered dividmg tongue 31. From a consideration of Figure 8 itwill be clear that when a plurality of the members Sil-31 are placedside by side-and secured in position by a suitablemortar, as at 32, theywill provide' a'serieslofupwardly, opening, aring channels Within whichthe electrical heating, element may be. disposed. From Figurey 8 it.w1llbe. clear that heat exchanged by radiation from the heating element Emay be accomplished through a fairly wlde angle because. of the areofthe space between adjacent'portions 31.

Insteadof the specialrefractory elementsv .3G-31 just described, we mayuse ordinary arch brick as shown at30a in Figures l13 to l5. inclusive.These archbrlcks, because they can be machine cast, are less expensiveandhave better physical characteristics than the members 30-31.

In order to preventthe heatingelement E from coming into contact withthe refractory portionsr31-v which would tendtocause themto burn out, wehave provided holders or spacers of insulating material, as shown 1nFigures 9 and l0 and indicated generally by the numerall 33. The members33 have-upwardly, opening, flaring slots indicated at 34 and the edgesofthe slots arechamfered, ,as bestseen at 35 inFigure 10. Therelationship between the members 33 and the. refractory members Sti-31is perhaps best seen in Figures 8 and l2. In Figure 8 it will beobserved that the bottom of the slots 34V is above the portions 34B ofthe refractory members so that theheating element E is spaced from the,bottom of the wide slot between the members 31. The chamfered edges 35of the slots 34 prevent the heating element E from falling. laterallyinto contact with the portions 31. Byvirtueofthe chamfered edges onlyavery small interference with heat radiation is occasioned by theirpresence. The' chamfers 35.- permit radiation tol both sides of theelements 33.

As seen in Figure 12 the elements 33 are provided in spaced relationshipbetween each set of the. members Sil- 31.-

In some cases it may. be desirable, in addition to the spacers 33, toprovide a supplementary spacer 33a as shownsin detail in Figure. 16, anddisposed as best seen in Figure 13. The use ofthemembers 33a furtherinsures that the ribbon of heatingl element will not tip and contactthe4 brick. The. members 33a are slotted as at 34u and the edges of. theslots are chamfered as at.35'a.

Asv clearly seen in Figure 7 the members Sil-31 or 30a: are placed uponthe refractory floor 11.. only to the extent of providing. a roughlycircular base upon which the member18 may rest, and by which the member18 and the coils may be supported. It willbe clear that. the looping.ofV the. heating element E back and forthasbest seen in Figures Sand 7,permits the. heating.

element to expand longitudinally with the expansion being taken up bythe loops at` theY end of the respective courses. If there. should be.any buckling of the heating element, the element will not come intocontact with the refractory material'31 by virtue of the spacing members33, which are ofa'sutable insulating material, such as porcelain,v forexample.

In Figure 13V we have shown how the members 30-31 or the members 30a maybe placed in a hollow rectangular formation. The structure is rnadestill stronger by the use: of'central blocks 40 of refractory materialto bear a portion of the load of the stools 18' and the columns ZOI andthusof the upper coils. This arrangement does not detract from theheating characteristics of the base because. there is no metal to beheated at the center of the coil.

By the construction disclosed herein the coils within the furnace arenot heated only by radiation from the walls of the annealing cover, ashas been general in the past, but. are also heated by radiation to thebases 18,.and by conduction from the bases 18 edgewise through thecoils. The edge-heating of the coils makes it possible for the. inside.convolutions of the coils to be heated as rapidly, or nearly as rapidlyas the outermost convolutionsso that a substantial and valuable.reduction in annealing time and improvement in uniformity is achieved.The. anneals for silicon steel coils are operations covering severaldays, and we have found that the annealing. time can be reduced. by asmuch as 20% or more because of the better and more uniform heating ofthe coils `resulting fromthe base heating-arrangementdisclosed herein.The necessary heat may be provided by an electrical input of about wattsper square inch, and under these conditions the life of the heatingelement E is perfectly normal. The construction disclosed, particularlyinvolving the use of the spacing elements 33 and 33a, makes it possibleto use Carborundum for the members 30-31 or 39a, which is advantageousbel and we, therefore, do not intend to limitourselves otherwisethan asset forth-in the claims-which follow.

Having now fully described our invention, what we claim as new, anddesireto secure by Letters Patent, is: l. An annealingfurnace basehaving heating means therein, comprising a sub-base of refractory brickand an upper layer of refractory elements, said last named elementshavingrectangular bases and upwardly narrowing dividing. portions, saidlast named elements being disposed in courses with their bases adjacenteachother.

. to provide between said courses upwardly facing flaring and a ribbonof electrical resistance material sinuously disposed in said slotsbetween said courses and supported by the slots in said separatormembers.

2. A structure according to claimv 1 wherein the refractory elements ofsaid upper layer have sidewalls which are inwardly oifset above theirbases, and themselves taper upwardly.

3. A structure according to claim l wherein the refractory elements ofsaid upper layer are trapezoidal in cross section.

4.. A structure according to claim 1 wherein the slots in saidtransverse separator members are provided with chamfered edges.

5. A structure according to claim l wherein supplementary transverseseparator members are disposed between the elements of said courses,providing downwardly facingflaring slots also aligned with rst mentionedslots.

6. A structure according to claim 5 whereinV the slots in saidtransverse separator members and said supplementary transverse separatormembers are provided with chamfered edges.

7. A structure according to claim 1 wherein said courses are ofdifferent lengths and are arranged to provide a sublstantially circularheating area for the annealing of co1 s.

8. A structure according to claim 1 wherein said courses are ofdifferent lengths and are arranged to provide a substantiallyrectangular heating areawith a central substantially circular supportingarea devoid of a heating element.

9. A structure according to claim 1 wherein said refractory elements areof a semi-conductive material havinghigh compressive strength.

l0. A structure according to claim 9 wherein said refractory elementsare of Carborundum.

1l. A structure according to claim l wherein said transverse separatormembers are of porcelain.

l2. A structure according to claim l wherein said refractory elementsare of semi-conductive material having a high compressive strength andwherein said transvtrse separator members are provided with chamfered eges.

13. A structure according to claim l2 wherein said courses are ofdifferent lengths and are arranged` to provide a substantially circularheating area for the annealing of coils.

14. A structure according to claim 12 wherein said courses are ofdifferent lengths and are arranged to provide a substantiallyrectangular heating area with a central substantially circularsupporting area devoid of a heating element.

(References on following page) Number UNITED STATES PATENTS Name DateHanson Dec. 13, 1927 5 McFarland Mar. 6, 1928 Mulrany Aug. 28, 1928Smalley June 10, 1930 Brown Aug. 9, 1932 Hanson Aug. 23, 1932 10 Number6 Name Date Rosenfeldt Nov. 24, 1936 Nordstrom Dec. 6, 1938 Norton Sept.9, 1941 Burdette Dec. 6, 1949 Stordey Apr. 3, 1951 OTHER REFERENCESGeneral Electric Review, May 1940, pp. 217-219.

